Two experiments investigated whether and how clear speech production enhances intelligibility of English fricatives for normal-hearing listeners and listeners with simulated hearing impairment. Fricative intelligibility in clear and conversational speech was assessed using a database of 8800 VCV ([a]-fricative-[a]) stimuli produced by 20 speakers. Babble thresholds were measured for minimal pair distinctions for 14 normal-hearing listeners and 14 listeners with simulated sloping, recruiting impairment. Clear speech benefited both groups overall; however, for impaired listeners, the clear speech effect held only for sibilant pairs. In a previous acoustic study involving the same stimuli [Maniwa, Jongman, and Wade, J. Acoust. Soc. Am. 119, 3301 (2006)], 14 parameters were measured: spectral peak location, the first four spectral moments, F2 onset transitions, spectral slopes below and above typical peak locations, pitch of adjacent vowels, overall rms amplitude, relative amplitude (frication amplitude relative to the vowel in specific frequency bands), harmonic-to-noise ratio, energy below 500 Hz, and fricative duration. Correlation analyses comparing acoustic and perceptual data indicated that a shift of energy concentration toward higher frequency regions and greater source strength contributed to the clear speech effect for normal-hearing listeners, while listeners with simulated loss seemed to benefit mostly from cues involving lower frequency regions.